We are measuring, in rats, the effects of purified dietary fiber components on intestinal transit time, intestinal microbiology, and the bioavailability of vitamine B12, folacin, zinc, calcium, and iron. Test fibers include cellulose, pectin, lignin, xylan, alginic acid, guar gum and wheat bran, and may extend to other fibers and fibrous foods. Overall utilization rate of micronutrients is determined by analysis of excretion and retention of radioactive tracer doses of the nutrients. Mechanisms of observed effects are investigated by in vitro binding studies and by comparison of data from germ-free and conventional rats in order to evaluate the involvement of intestinal microbial metabolism. In cases where intestinal bacteria appear to be involved, further examinations of fecal enzymology and bacterial profile and counts are carried out in order to clarify the mechanisms.